AMES, Iowa - Research continues to increase the effectiveness of best management practices (BMPs) for improving water quality, while seeking to make practices cheaper and easier for landowners to install, say researchers at Iowa State University.
Saturated buffers
Tom Isenhart, professor of natural resource ecology and management, is known for his work to help develop and refine the use of saturated buffers as an edge-of-field conservation practice that filters water flowing from farm drain tiles. He also studies other BMPs, including saturated grass waterways, a new practice being developed with colleagues at the University of Iowa.
He leads water quality research at more than 15 field-scale locations that represent almost 100 site years of data. That record, which includes locations going back to 2010, is valuable in various ways, such as tracking practice effectiveness through year-to-year weather variability, according to Isenhart.
His work, often supported by the Iowa Nutrient Research Center, mainly focuses on using BMPs to reduce nitrate-nitrogen, a pollutant addressed in the Iowa Nutrient Reduction Strategy. Isenhart and colleagues are also looking at the potential of BMPs to reduce phosphorus, the other main concern of the INRS.
“People often focus on an edge-of-field BMP’s ability to reduce nutrient concentration from the point water flows into the BMP for treatment to where it leaves and enters a waterway or ditch,” he said. “However, what really has the most significant impact on water quality is how much water flows through the practice.”
“If a BMP can capture a lot of flow, you gain a much greater reduction in the mass of nitrogen it treats, even if the reduction in concentration is lower,” he said. “Tracking a variety of parameters, which include flow, increases confidence that our results realistically reflect different locations and conditions.”
“We also need more monitoring at the small watershed scale where enough practices have been installed that we might be able to see the needle moving – and then compare over time to similar paired watersheds that don’t have many practices,” he said. “It’s fairly easy to see improvements from individual practices, but does that hold up at the watershed level?”
This kind of research is critically important to demonstrate results that can be expected from practice implementation, but it can be hard to set up and fund, according to Isenhart.
Bioreactors
Iowa State Professor Michelle Soupir, agricultural and biosystems engineering, is one of the country’s leading researchers studying water quality bioreactors and how to make them effective and practical. Much of her work has also received INRC support.
A bioreactor is an edge-of-field water-treatment technology used to remove nitrate in tile drainage coming from crop fields. Water piped into a plastic-lined trench interacts with a high-carbon material. The bioreactor environment supports microbes that transform nitrate into harmless nitrogen gas. Water leaves the bioreactor cleaner before it flows to waterways or ditches.
In 2014, Soupir’s lab team designed and installed a unique pilot bioreactor system on a research farm near Ames. There, nine mini bioreactors filled with wood chips were closely monitored from inflow to outflow. Over the years, the bioreactors removed from 9-54% of the incoming nitrate concentration, depending on conditions like flow rate and temperature.
When water flows through more quickly during wet weather, the bioreactor may remove a lower percentage of nitrogen from the tile water, yet still reduce a larger overall pollutant load, Soupir said, echoing a point emphasized by Isenhart.
Bioreactors started gaining prominence as an edge-of-field practice for nitrate reduction with their inclusion in the Iowa Nutrient Reduction Strategy science assessment, and the technology is catching on in other states with extensive agricultural drainage.
“We’ve started to get enough bioreactors on the ground to potentially move the needle in some watersheds," Soupir said. "With additional funding from a variety of sources, we’re working around the state with Batch and Build type projects, pioneered by the Polk County, Iowa, Soil and Water Conservation District and the Iowa Soybean Association. At this point, 24 new bioreactors are designed, 15 installed and nine more are planned. We’re also running tracer studies on these to continue to follow their hydraulic properties and water quality benefits.”
More recently, her lab and other Iowa State researchers have been exploring the potential of other carbon sources, including corn cobs. Results so far suggest the corn cobs initially outperform wood chips but likely reduce nitrates at roughly the same level after five or six years.
The estimated cost to install a bioreactor ranges from $15,000 to $30,000 depending primarily on size and carbon source.
“At a time when farmers are facing major economic challenges, it’s more important than ever to provide good guidance to make sure that conservation practices will provide the desired return on investment for private – and public – dollars,” Soupir said.
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Contacts
Tom Isenhart, Natural Resource Ecology and Management, 515-294-8056, isenhart@iastate.edu
Michelle Soupir, Agricultural and Biosystems Engineering, 515-294-2307, msoupir@iastate.edu
Ann Y. Robinson, Agriculture and Life Sciences Communications, 515-294-3066, ayr@iastate.edu